Air Conditioning Compressors
p e r a t u r e , q u a l i t y a n d m o v e m e n t i n a l l c o r n e r s
o f t h e v e h i c l e . T h e m o d e r n h e a t i n g , v e n t i l a -
t i n g a n d a i r c o n d i t i o n i n g s y s t e m ( H VAC ) c a n
e n s u r e t h a t t h e r m a l c o m f o r t a n d a l l r o u n d
v i s i b i l i t y a r e d e l i v e r e d i n e n v i r o n m e n t s t h a t
r a n g e f r o m t h e h e a t o f P h o e n i x A r i z o n a t o
t h e c o l d e s t S c a n d i n a v i a n w i n t e r.
I n t r o d u c t i o n
T h e p a s s e n g e r c o m p a r t m e n t o f a m o d e r n
a u t o m o b i l e o ffe r s a v e r y d i ffe r e n t e n v i r o n -
m e n t t o t h a t o f a v e h i c l e f r o m f i ft y y e a r s
a g o . A s w e l l a s t h e e r g o n o m i c a l l y d e s i g n e d
s e a t i n g a n d i n s t r u m e n t l a y o u t , t h e a l l r o u n d
v i s i b i l i t y a n d t h e e ff i c i e n t u s e o f s p a c e ,
t o d a y ’s p a s s e n g e r h a s c o n t r o l o v e r a i r t e m -
V i e w o f i n s t r u m e n t p a n e l a n d H VAC c o n t r o l s
E x p a n d e d v i e w o f a m o d e r n
H VAC c o m p r e s s o r
T h e v e r y h e a r t o f t h e a i r c o n d i t i o n i n g s y s -
t e m i s t h e c o m p r e s s o r. I t s k e y t a s k s a r e t o
g e n e r a t e t h e r e q u i r e d f l o w o f r e f r i g e r a n t
a r o u n d t h e s y s t e m a n d a t t h e s a m e t i m e
t o c o m p r e s s i t s u ff i c i e n t l y t o r a i s e i t s
t e m p e r a t u r e a b o v e t h e a m b i e n t i n o r d e r
t h a t h e a t c a n b e r e j e c t e d f r o m t h e s y s t e m .
T h e s e d e m a n d s m u s t b e m e t e ff i c i e n t l y o v e r
v e r y w i d e r a n g e s o f c o m p r e s s o r s p e e d a n d
a m b i e n t c o n d i t i o n s . A t t h e s a m e t i m e v e r y
d e m a n d i n g n o i s e g e n e r a t i o n c o n s t r a i n t s a n d
e x p e c t a t i o n s o f d u r a b i l i t y h a v e t o b e m e t .
A i r C o n d i t i o n i n g
C y c l e
I t i s s e l f e v i d e n t t h a t h e a t t e n d s t o f l o w
f r o m h i g h t e m p e r a t u r e t o l o w. I f w e w i s h t o
p r o v i d e c o o l i n g a t a l o c a t i o n i n a h i g h t e m p e -
r a t u r e e n v i r o n m e n t t h e n w e a r e e ffe c t i v e l y
a s k i n g h e a t t o f l o w f r o m l o w t e m p e r a t u r e
t o h i g h . To a ch i e v e t h i s i t i s n e c e s s a r y t o
o p e r a t e a t h e r m o d y n a m i c c y c l e i n w h i ch a
r e f r i g e r a n t a t a l o w t e m p e r a t u r e i s u s e d t o
e x t r a c t h e a t f r o m t h e l o c a t i o n t o b e c o o l e d .
T h e r e f r i g e r a n t i s s u b s e q u e n t l y c o m p r e s s e d
u n t i l i t b e c o m e s h o t e n o u g h t o b e a b l e t o
r e j e c t h e a t t o t h e a m b i e n t . A ft e r c o o l i n g t o
n e a r a m b i e n t t e m p e r a t u r e b y t h e a m b i e n t
a i r, i t i s e x p a n d e d b a ck t o l o w p r e s s u r e , a
p r o c e s s w h i ch g e n e r a t e s f u r t h e r r e f r i g e r a n t
t e m p e r a t u r e r e d u c t i o n t h a t b e c o m e s l o w
e n o u g h t o b e u s e d f o r c o o l i n g a t t h e r e -
q u i r e d l o c a t i o n . T h e c y c l e i s c o m p l e t e . T h e
required cooling is thus achieved but at the expense of the work necessary to drive the compressor.
The Automotive
Air Conditioning
Application
The automotive application places very special demands on the air conditioning system. A typical vehicle system has a similar cooling capacity to that required for the air conditioning of a small house despite the vast difference in volumes to be cooled. The reasons for this are twofold. Firstly cooling duty per unit volume is much higher for the vehicle because heat transfer coefficients between hot ambient air and the outside surfaces are much higher due to movement of the vehicle through the air. Secondly the proportion of the enclosure consisting of glass is very high for the vehicle – a factor that makes the effect of direct solar radiation heating very high. On top of this a particularly demanding requirement is to cool the cabin very rapidly after the vehicle has been soaked in an ambient temperature of 40°C or higher. At the start of the cool down temperatures in the cabin can be as high as 60 or 70°C.
Another significant way in which automotive air conditioning differs from the domestic or commercial version is the question of compressor drive. In the vehicle the compressor is belt driven by the engine so that independent control over the compressor speed is not possible. This obviously has significant implications for system control and means that there can be calls for high system performance at times when the compressor speed is very low. An important
The challenge of compressor packaging
implication of this is that the compressor drive shaft must pass out of the compressor casing with the resultant potential for refrigerant leakage. Hermetic compressors are not possible and very effective shaft seals must be used. A second implication of the external drive is that the compressor must be engine mounted so that lengths of flexible hose must be introduced to accommodate relative movement between engine and chassis mounted components.
As with other air conditioning applications system efficiency is very important and the
automotive application is no exception. While
the characteristics of all the major components in the system contribute to overall efficiency any compressor inefficiencies must be kept to a minimum. A further feature of the compressor that requires serious consideration is its intrinsic noise generation - modern vehicle noise requirements mean that the compressor must be very quiet and vibration free.
And finally, three further requirements of the compressor, specific to the automotive application, but which apply equally to every vehicle component – are stringent con-straints on size, weight and cost.
As a result of all these constraints deriving from the use of an engine driven compressor, it is often suggested that an electrically driven system would provide a much better solution. The reason that it is not feasible on current vehicles is insufficient electrical power is available and its application must await the widespread implementation of high
powered and efficient integrated starter/
generators. The applications in which an electrical compressor would make real sense however are in hybrid and fuel cell vehicles where sufficient electrical power is readily available.
h
eat rejected to ambientexpansion deviceheat absorbed from cabincondenserevaporatorcompressor
Schematic of air conditioning cycle
D e l p h i v e h i c l e w i t h H e a t P u m p s u p p l e m e n t a r y h e a t i n g
T h e h i g h e ff i c i e n c y o f m o d e r n e n g i n e s c a n
l e a d t o t h e s i t u a t i o n i n w h i ch i n s u ff i c i e n t r e -
j e c t e d h e a t i s a v a i l a b l e f o r c o m f o r t h e a t i n g .
T h i s f a c t h a s p r o m p t e d t h e s u g g e s t i o n t h a t
t h e a i r c o n d i t i o n i n g s y s t e m b e o p e r a t e d i n
r e v e r s e a s a h e a t p u m p t o s u p p l e m e n t t h e
e n g i n e h e a t a n d t h e v i a b i l i t y o f t h e c o n c e p t
h a s b e e n d e m o n s t r a t e d o n a n u m b e r o f p l a t -
f o r m s . T h e i m p l i c a t i o n s f o r t h e c o m p r e s s o r
a r e t h a t t h e r e q u i r e d o p e r a t i n g l i fe c a n b e
n e a r l y d o u b l e d a n d t h e c o m p r e s s o r a m b i e n t
s a fe o p e r a t i n g t e m p e r a t u r e r a n g e m u s t b e
e x t e n d e d d o w n w a r d s t o m i n u s 2 0 ° C .
R e f r i g e r a n t I s s u e s
T h e a u t o m o t i v e a i r c o n d i t i o n i n g i n d u s t r y
r e s p o n d e d p r o - a c t i v e l y t o t h e d e m a n d s o f
t h e 19 8 7 M o n t r e a l P r o t o c o l a n d b y 19 9 4 ,
2 y e a r s e a r l y, t h e ch a n g e o v e r f r o m R 12 t o
R 13 4 a w a s c o m p l e t e f o r a l l v e h i c l e p r o d u c -
t i o n l i n e s i n t h e d e v e l o p e d w o r l d . I t s o o n
b e c a m e a p p a r e n t t h a t t h i s m a y n o t b e t h e
e n d o f t h e s t o r y a n d w i t h i n c r e a s i n g p e n e -
t r a t i o n o f a i r c o n d i t i o n i n g i n t h e E u r o p e a n
m a r k e t t o g e t h e r w i t h t h e d e m a n d s o f t h e
Ky o t o P r o t o c o l p r e s s u r e h a s b u i l t t o m a k e
ch a n g e s t o s t i l l f u r t h e r r e d u c e t h e p o t e n t i a l
c o n t r i b u t i o n o f a i r c o n d i t i o n i n g s y s t e m s
t o g l o b a l w a r m i n g . A n e w D i r e c t i v e h a s
r e c e n t l y c o m p l e t e d i t s p r o g r e s s t h r o u g h t h e
E u r o p e a n l e g i s l a t i v e p r o c e s s . I t r e q u i r e s t h e
e l i m i n a t i o n o f R 13 4 a f r o m a l l n e w m o d e l s
f r o m 2 011 a n d f r o m a l l n e w v e h i c l e s b y 2 017.
T h e c u r r e n t l y c o n s i d e r e d a l t e r n a t i v e s a r e
R 15 2 a w i t h a g l o b a l w a r m i n g p o t e n t i a l l e s s
t h a n 10 % o f t h a t o f R 13 4 a , o r t h e s o - c a l l e d
‘ n a t u r a l ’ r e f r i g e r a n t R 74 4 ( c a r b o n d i o x i d e ) .
R 15 2 a h a s t h e r m o d y n a m i c ch a r a c t e r i s t i c s
v e r y s i m i l a r t o t h o s e o f R 13 4 a a n d w i l l b e
d i r e c t l y u s a b l e w i t h c u r r e n t c o m p r e s s o r
t e ch n o l o g y. I t s p o t e n t i a l d r a w b a ck i s a
d e g r e e o f f l a m m a b i l i t y t h a t h a s m a d e t h e
i n d u s t r y r e l u c t a n t t o c o n s i d e r i t . M o r e r e -
c e n t l y o t h e r l a r g e ch e m i c a l c o m p a n i e s h a v e
a n n o u n c e d t h e p o t e n t i a l a v a i l a b i l i t y o f n e w
a l t e r n a t i v e s . L i tt l e i s k n o w n a b o u t t h e m a t
t h i s s t a g e b u t i t i s a s s u m e d t h a t t h e y t o o
w o u l d f u n c t i o n w i t h c u r r e n t c o m p r e s s o r
t e ch n o l o g y. T h e r e m u s t b e a q u e s t i o n a s t o
w h e t h e r t h e n e c e s s a r y d e v e l o p m e n t a n d
100 200 300 400 500 600 700
1
10
100
Enthalpy - kJ/kg
Pressure - MPa
-40°C
0°C
40°C
80°C 120°C 160°C 200°C
200°C
160°C
120°C
80°C
40°C
0°C
I d e a l i z e d p r e s s u r e e n t h a l p y d i a g r a m o f C O 2 c y c l e
t e s t i n g a n d t h e n i m p l e m e n t a t i o n o f t h e
n e c e s s a r y m a n u f a c t u r i n g c a p a c i t y c a n b e
c o m p l e t e d i n t i m e t o m e e t t h e r e q u i r e m e n t s
o f t h e E u r o p e a n l e g i s l a t i o n . I f R 74 4 b e c o m e s
t h e ch o s e n r o u t e t h e i m p l i c a t i o n s f o r c o m -
p r e s s o r t e ch n o l o g y a r e v e r y f a r- r e a ch i n g . A i r
c o n d i t i o n i n g s y s t e m s w i t h R 74 4 n e e d c o m -
p r e s s o r s w i t h d i s p l a c e m e n t o f o n l y a f i ft h
o f t h a t r e q u i r e d f o r R 13 4 a b u t o p e r a t i n g a t
mu ch h i g h e r p r e s s u r e s . D i s ch a r g e p r e s s u r e s
o f 12 0 b a r a r e n o rma l c omp a r e d w i t h a t y p i -
c a l 18 b a r f o r a n R 13 4 a s y s t em. A s c a n b e
ima g i n e d , t h e s e f a c t o r s h a v e b i g imp l i c a t i o n s
f o r t h e c omp r e s s o r l a y o u t a n d s t ru c tu r a l
s t r e n g t h r e q u i r eme n t s a n d a l s o r e p r e s e n t a
p a r t i c u l a r l y s e v e r e s h a ft s e a l ch a l l e n g e .
A n e a r l y
c o m p r e s s o r,
t h e D e l p h i R 4
C o m p r e s s o r
T e c h n o l o g i e s
A i r c o n d i t i o n i n g b e g a n t o b e c o m e a v a i l a b l e
f o r v e h i c l e s i n t h e e a r l y 19 5 0 s . Fr o m t h e
b e g i n n i n g a n u m b e r o f d i ffe r e n t c o m p r e s s o r
t e ch n o l o g i e s h a v e b e e n u s e d . T h e e a r l i e s t
s y s t e m s u s e d p i s t o n c o m p r e s s o r s i n v a r i o u s
c o n f i g u r a t i o n s . T h e Fr i g i d a i r e F 5 , a f i v e p i s -
t o n w o b b l e p l a t e c o n f i g u r a t i o n , u s e d i n t h e
e a r l i e s t G M v e h i c l e s w i t h a i r c o n d i t i o n i n g
w a s f i r s t p r o d u c e d i n 19 5 6 – i t w e i g h e d i n a t
1 8 k g ! T h e R 4 c o m p r e s s o r w i t h a s c o t ch y o k e
m e ch a n i s m w a s f i r s t p r o d u c e d b y H a r r i s o n
( n o w D e l p h i ) i n 19 74 a n d r e m a i n e d i n p r o -
d u c t i o n u n t i l 19 9 5 . I t w a s 19 0 m m i n o v e r a l l
d i a m e t e r a n d w e i g h e d 9 k g .
S e c t i o n t h r o u g h a n e a r l y f i x e d s w a s h - p l a t e
c o m p r e s s o r, t h e D e l p h i H D 6
I l l u s t r a t i o n o f S c r o l l c o m p r e s s i o n p r o c e s s
T h e m e ch a n i s m o f a v a r i a b l e w o b b l e p l a t e c o m p r e s s o r
T h e p r e fe r r e d c o n f i g u r a t i o n f o r a p i s t o n
c o m p r e s s o r s o o n m o v e d t o a d o u b l e a c t i n g
s w a s h - p l a t e d e s i g n o f w h i ch t h e H a r r i s o n
( D e l p h i ) H D 6 i s t y p i c a l . T h e f i x e d s w a s h -
p l a t e i s h e l d b e t w e e n t h e o p p o s i n g e n d s
o f t h e d o u b l e p i s t o n b y a p a i r o f s h o e s a n d
t w o s t e e l b a l l s .
A s e c o n d p o s i t i v e d i s p l a c e m e n t c o n f i g u r a -
t i o n u s e d i s t h e s l i d i n g v a n e . I t o ffe r s a d -
v a n t a g e s o f c o m p a c t n e s s a n d l o w c o s t b u t
c a r r i e s t h e p e n a l t y o f v e r y p o o r e ff i c i e n c y a t
h i g h p r e s s u r e r a t i o s .
T h e o t h e r m a i n c o n f i g u r a t i o n i s t h e s c r o l l
c o m p r e s s o r i n w h i ch o n e s c r o l l w i t h a n i n -
v o l u t e s u r f a c e o r b i t s i n s i d e a f i x e d s e c o n d
s c r o l l o f t h e s a m e s h a p e . I t c a n b e s e e n
f r o m t h e f i g u r e t h a t t h e c o n t a c t p o i n t s o f
t h e s c r o l l s e n c l o s e a c a v i t y o f r e d u c i n g s i z e
( s h a d e d g r e e n ) t h a t m o v e s f r o m t h e o u t s i d e
t o t h e c e n t r e a s t h e o n e s c r o l l o r b i t s i n s i d e
t h e o t h e r. T h e r e s u l t i s a n i n d u c t i o n o f g a s
a t t h e p e r i p h e r y o f t h e s c r o l l a n d d e l i v e r y
o f c o m p r e s s e d g a s a t t h e c e n t r e . T h e s e
c o m p r e s s o r s a r e v e r y e ff i c i e n t a n d q u i e t
b u t r e p r e s e n t a s i g n i f i c a n t ch a l l e n g e f o r
m a n u f a c t u r e a n d h e n c e f o r c o s t . T h e y h a v e
t h e d i s a d v a n t a g e t h a t a l t h o u g h a v a r i a b l e
v e r s i o n o f t h i s c o m p r e s s o r i s p o s s i b l e , t h e
s u p e r i o r e ff i c i e n c y a d v a n t a g e i s l o s t .
E a r l y c o m p r e s s o r s w e r e a l l f i x e d d i s p l a c e -
m e n t a n d s y s t e m c o n t r o l w a s a ch i e v e d b y
s w i t ch i n g t h e c o m p r e s s o r o n a n d o ff b y
m e a n s o f a n e l e c t r o - m e ch a n i c a l c l u t ch
c o n t a i n e d w i t h i n t h e c o m p r e s s o r p u l l e y.
A s c o n s i d e r a t i o n b e g a n t o b e g i v e n t o t h e
a p p l i c a t i o n o f a i r c o n d i t i o n i n g t o s m a l l e r
v e h i c l e s w i t h s m a l l e r e n g i n e s i t w a s f o u n d
t h a t t h e s i g n i f i c a n t a n d s u d d e n i n c r e a s e i n
e n g i n e l o a d t h a t r e s u l t e d f r o m c o m p r e s s o r
s w i t ch i n g c a u s e d p r o b l e m s f o r t h e s m a l l
e n g i n e w i t h r e s u l t a n t i s s u e s o f d r i v a b i l i t y.
A c o m p r e s s o r w i t h v a r i a b l e d i s p l a c e m e n t
o ffe r e d t h e s o l u t i o n t o t h i s p r o b l e m . I n 19 8 5
H a r r i s o n ( D e l p h i ) w e r e t h e f i r s t t o g o i n t o
s e r i e s p r o d u c t i o n w i t h a v a r i a b l e c o m p r e s -
s o r, t h e V 5 , a w o b b l e p l a t e d e s i g n w i t h f i v e
p i s t o n s .
A l t h o u g h s c r o l l , v a n e a n d p i s t o n c o m p r e s -
s o r s a r e a l l s t i l l i n u s e i n a u t o m o t i v e a p p l i c a -
t i o n s , t h e p i s t o n c o m p r e s s o r i s d o m i n a n t .
W h e r e t h e c o m b i n a t i o n o f e ff i c i e n c y a n d
c o n t r o l l a b i l i t y i s t h e k e y r e q u i r e m e n t , p i s t o n
c o m p r e s s o r s o ffe r t h e b e s t s o l u t i o n .
P i s t o n C o m p r e s s o r s
T h e c o m p r e s s o r h a s t h e t a s k o f i n d u c i n g g a s
a t a l o w s u c t i o n p r e s s u r e a n d d e l i v e r i n g i t a t
a h i g h e r d i s ch a r g e p r e s s u r e . I t a ch i e v e s t h i s
b y u s i n g r e e d v a l v e s t h a t o p e r a t e a u t o m a -
t i c a l l y t o c o n t r o l t h e f l u i d f l o w i n t o a n d o u t o f
t h e c y l i n d e r s . S t a r t i n g w i t h t h e p i s t o n a t t o p
d e a d c e n t r e t h e p r e s s u r e i n t h e s m a l l c l e a ra
n c e v o l u m e w i l l b e c l o s e t o t h e d i s ch a r g e
p r e s s u r e a s t h e p i s t o n h a s j u s t d e l i v e r e d i t s
ch a r g e . A s t h e p i s t o n r e c e d e s a n d t h e p r e s -
s u r e i n t h e c l e a r a n c e v o l u m e f a l l s , t h e d e l i v e -
r y r e e d v a l v e c l o s e s a u t o m a t i c a l l y, d r i v e n b y
t h e d i s ch a r g e p r e s s u r e . S i n c e t h e c l e a r a n c e
C
ylinder volume - cm3discharge pressure Pdsuction pressure Ps05101520251051520Cylinder Pressure -
bar
Indicator diagram for swash-plate compressor
volume is small, the pressure drops quickly
until it is below the suction pressure. At this stage the intake valve opens and the further movement of the piston induces fresh charge.
After bottom dead centre the piston compresses the gas induced into the cylinder until it reaches the discharge pressure. At this stage the delivery valve is opened automatically by the pressure differential and the compressed charge is delivered.
There are several key features of this overall process important for performance and efficiency. The clearance volume must be as
small as possible without risking interference between the piston and the cylinder head as a result of differential thermal expan-sion or stress effects. The consequences of finite clearance volume are principally indicated by the compressor volumetric efficiency which is the ratio of the volume of delivered gas measured at the suction pressure relative to volume displaced by the
piston. The dynamic response characteristics of the reed valves are also important. Volumetric efficiency is also impacted by the quantity of gas that leaks past the pistons to the crank case, which is determined by piston sealing and clearances.
Efficiency Definition
volumetric ηv delivered volume
displaced volume
ideal minimum work needed
isentropic ηs work done to compress gas
work done on compressed gas
mechanical ηm work input to compressor shaft
Table of compressor efficiencies
The second measure of compressor performance quality is the isentropic efficiency. It is given by the ratio of the theoretical minimum work required to compress the gas from suction to discharge pressure relative to the work actually done. The theoretical minimum is based on an idealized ‘isentropic’ process in which no turbulence genera-tion or viscosity effects occur. The third measure of compressor performance quality is the mechanical efficiency. This is the ratio of the work actually done on the gas relative to the measured power input to the compressor shaft. The difference between these two figures is due to friction.
Variable Piston
Compressors
As stated above, Harrison (now Delphi) was the first to go into series production with a variable compressor. The wobble plate that drives the pistons with this design is free to tilt so that the piston stroke, and hence displacement can be changed. The wobble plate mechanism allows very short and compact pistons to be used. The ball-ended connecting rods are swaged into the pistons and wobble plate which results in strong, low friction and very simple joints. The fact that the connecting rods are tilted slightly during compression as a result of the wobble plate movement means that the forces act-ing do not all lie along the piston axes. The result is that higher vibrational harmonics can be generated which makes management of compressor noise more of a challenge than with later generations of swash-plate compressor. Nonetheless the value of this configuration is illustrated by the fact that it is still produced at a rate of several million units per year worldwide for installation in new vehicles as original equipment, offering a good compromise between cost and the functionality of a variable displacement com-pressor.
The next generation of variable compressors used a swash-plate mechanism, largely because of its advantages of low vibration and noise. The mechanism by which the compressor displacement is controlled can be described in principle relatively simply, but in fact the actual displacement of the compressor in any given situation results from a quite complex interaction of forces.
Va r i a b l e s w a s h - p l a t e c o m p r e s s o r s h o w i n g m e ch a n i s m
Ta b l e o f s w a s h - p l a t e t o r q u e g e n e r a t i n g m e ch a n i s m s
T h e s w a s h - p l a t e h a s a l i n k a g e m e ch a n i s m
t h a t a l l o w s i t t o r o t a t e t h u s ch a n g i n g i t s a n -
g l e a n d w i t h i t , t h e p i s t o n d i s p l a c e m e n t . T h e
l i n k a g e i s d e s i g n e d s o t h a t t h e c l e a r a n c e
v o l u m e r e m a i n s a s c o n s t a n t a n d s m a l l a s
p o s s i b l e o v e r t h e f u l l s w a s h - p l a t e a n g l e
r a n g e f r o m f u l l s t r o k e t o m i n i m u m s t r o k e .
T h i s s w a s h - p l a t e s f r e e d o m t o r o t a t e m e a n s
t h a t u n d e r a n y g i v e n o p e r a t i n g c o n d i t i o n s
i t w i l l t a k e u p a p o s i t i o n t h a t i s d e t e r m i -
n e d b y t h e b a l a n c e o f a l l t h e f o r c e s a c t i n g
o n i t t h a t t e n d t o c a u s e i t t o r o t a t e a b o u t
i t s c e n t r e o f r o t a t i o n . T h e f i r s t e l e m e n t o f
c o m p l e x i t y i s t h a t t h e c e n t r e o f r o t a t i o n i s
n o t f i x e d a s i t s h i ft s l o c a t i o n s l i g h t l y w i t h
t h e s w a s h - p l a t e a n g l e . I t l i e s f a i r l y n e a r t o
t h e s w a s h - p l a t e c o n n e c t i o n w i t h t h e l i n k b u t
i t s e x a c t l o c u s i s a f u n c t i o n o f t h e l i n k a g e
m e ch a n i s m l o c a t i o n , d i m e n s i o n s a n d o f t h e
s w a s h - p l a t e a n g l e . T h e m o s t o b v i o u s f o r c e
t h a t c o m e s i n t o p l a y i s t h e g a s p r e s s u r e
a c t i n g o n t h e p i s t o n c r o w n . E s t i m a t i o n o f
i t s a v e r a g e e ffe c t , h o w e v e r i s c o m p l e x a s
t h e c y l i n d e r p r e s s u r e v a r i e s g r e a t l y a r o u n d
t h e c y c l e . A t t h e s a m e t i m e i t s l i n e o f a c t i o n
i s c o n t i n u a l l y ch a n g i n g a n d h e n c e s o i s t h e
e ffe c t i v e t o r q u e i t e x e r t s a b o u t t h e c e n t r e
o f r o t a t i o n . T h i s t o r q u e w i l l o b v i o u s l y t e n d
t o u p s t r o k e t h e c o m p r e s s o r.
A l e s s o b v i o u s s o u r c e o f t o r q u e g e n e r a t i o n
o n t h e s w a s h - p l a t e i s t h e i n e r t i a o f t h e p i s -
t o n s w h i ch a r e r e p e a t e d l y a c c e l e r a t e d a n d
d e c e l e r a t e d a s t h e c o m p r e s s o r i s o p e r a t e d .
I t m i g h t b e t h o u g h t t h a t t h e e ffe c t o f t h e
f o r c e s f o r a c c e l e r a t i o n a n d d e c e l e r a t i o n
c a n c e l e a ch o t h e r o u t b u t i n f a c t t h e p i s t o n
i s a c c e l e r a t e d u p w a r d s o v e r t h e h a l f o f t h e
s w a s h - p l a t e f u r t h e s t f r o m i t s c e n t r e o f r o t a -
t i o n a n d c o r r e s p o n d i n g l y d e c e l e r a t e d o v e r
t h e h a l f n e a r e s t t o t h e c e n t r e o f r o t a t i o n .
T h e f o r m e r t h e r e f o r e e x e r t s g r e a t e r t o r q u e
a n d t h e n e t r e s u l t i s a t e n d e n c y t o u p s t r o k e
w h i ch i s p r o p o r t i o n a l t o t h e s q u a r e o f t h e
p i s t o n s p e e d a n d t h u s b e c o m e s s i g n i f i c a n t
a t h i g h e r c o m p r e s s o r s p e e d s .
A s e c o n d t o r q u e g e n e r a t i n g f o r c e t h a t i s a
s i m i l a r f u n c t i o n o f c o m p r e s s o r s p e e d c o m e s
f r o m c e n t r i f u g a l a ffe c t s a c t i n g o n b o t h t h e
l i n k m e ch a n i s m a n d t h e s w a s h - p l a t e i t s e l f. I f
o n e c o n s i d e r s t h e t w o h a l v e s o f t h e s w a s h -
p l a t e n e a r e s t a n d m o s t r e m o t e f r o m t h e c e n -
t r e o f r o t a t i o n i t i s c l e a r t h a t t h e c e n t r i f u g a l
f o r c e s o f t h e m o r e r e m o t e h a l f g e n e r a t e t h e
g r e a t e r t o r q u e a n d t h e n e t r e s u l t w i l l b e a
t e n d e n c y t o d e s t r o k e t h e c o m p r e s s o r.
Fu r t h e r f o r c e s g e n e r a t i n g r o t a t i o n t o r q u e
c a n c o m e f r o m t h e f i tt i n g o f u p s t r o k e a n d / o r
d o w n s t r o k e s p r i n g s . T h e s e c a n b e i n s t a l l e d
o n t h e s h a ft t o a s s i s t t h e u p s t r o k e / d o w n -
s t r o ke p r o c e s s u n d e r s ome c omp r e s s o r o p e r a -
t i n g c o n d i t i o n s a n d i f f i tt e d w i l l o b v i o u s l y
c o n t r i b u t e t o t h e o v e r a l l b a l a n c e o f t o r q u e s .
H e r e t h e e ffe c t w i l l b e a s i m p l e f u n c t i o n o f
t h e s w a s h - p l a t e a n g l e .
T h e f i n a l c o n t r i b u t o r t o t h e b a l a n c e o f t o rq
u e s i s t h a t g e n e r a t e d o n t h e u n d e r s i d e
o f t h e p i s t o n s b y t h e c r a n k c a s e p r e s s u r e .
A l t h o u g h t h e c r a n k c a s e p r e s s u r e r e m a i n s
c o n s t a n t a r o u n d t h e c y c l e i t s l i n e o f a c t i o n
a r o u n d t h e p l a t e m u s t b e i n t e g r a t e d t o o b -
t a i n a n a v e r a g e n e t t o r q u e . I t i s t h e a b i l i t y t o
c o n t r o l t h i s p r e s s u r e t h a t a l l o w s t h e b a l a n c e
t o b e s h i ft e d a n d t h u s t h e s w a s h - p l a t e a n g l e
t o b e c o n t r o l l e d . C r a n k c a s e p r e s s u r e i s c o n -
t r o l l e d w i t h b l e e d s f r o m b o t h s u c t i o n a n d
h i g h s i d e . T h e s m a l l s u c t i o n b l e e d i s u s u a l l y
p e r m a n e n t a n d t h e h i g h s i d e b l e e d i s c o n -
t r o l l e d b y m e a n s o f a v a l v e . I f t h e h i g h s i d e
b l e e d i s c l o s e d t h e s u c t i o n b l e e d p u m p s t h e
c r a n k c a s e d o w n t o s u c t i o n p r e s s u r e w i t h t h e
r e s u l t t h a t t h e c o m p r e s s o r o p e r a t e s a t f u l l
M e c h a n i s m E f fe c t C o m m e n t
C y l i n d e r p r e s s u r e U p s t r o k e I n t e g r a t e d a r o u n d s w a s h - p l a t e
P i s t o n i n e r t i a U p s t r o k e S i g n i f i c a n t a t h i g h s p e e d
C e n t r i f u g a l f o r c e s D e s t r o k e S i g n i f i c a n t a t h i g h s p e e d
S p r i n g s U p s t r o k e / d e s t r o k e W h e r e f i tt e d
C r a n k c a s e p r e s s u r e D e s t r o k e A d j u s t e d f o r c o n t r o l
C o m p r e s s o r c o n t r o l c u r v e s
S e c t i o n t h r o u g h
p n e u m a t i c c o m p r e s s o r
c o n t r o l v a l v e
s t r o k e . I f t h e d i s ch a r g e p r e s s u r e g e t s t o o
h i g h , t h e h i g h p r e s s u r e b l e e d c a n b e o p e n e d
a n d t h e c r a n k c a s e p r e s s u r e i n c r e a s e s . A t
s o m e s t a g e i t w i l l b e h i g h e n o u g h f o r t h e
b a l a n c e o f t o r q u e s t o d e s t r o k e t h e c o m p r e s -
s o r. T h e c o n t r o l h a s b e e n a ch i e v e d .
T h e h i g h p r e s s u r e c o n t r o l v a l v e c a n b e a n
a u t o m a t i c , s p r i n g o p e r a t e d v a l v e o r a n e l e c -
t r i c a l l y s w i t ch e d a n d e l e c t r o n i c a l l y c o n t r o l -
l e d v a l v e . T h e f o r m e r c o n f i g u r a t i o n i s k n o w n
a s p n e u m a t i c c o n t r o l , t h e l a tt e r i s c a l l e d
e x t e r n a l c o n t r o l .
T h e d o m i n a n t e l e m e n t o f s y s t e m c o n t r o l
i s t h e t h e r m a l e x p a n s i o n v a l v e t h a t a c t s t o
m a i n t a i n a g i v e n d e g r e e o f s u p e r h e a t o f t h e
r e f r i g e r a n t l e a v i n g t h e e v a p o r a t o r. I f t h e
e v a p o r a t o r p r e s s u r e b e c o m e s t o o l o w a n d
t h e r i s k o f e v a p o r a t o r f r e e z i n g o c c u r s , t h e
p n e u m a t i c c o n t r o l v a l v e c o m e s i n t o o p e r a -
t i o n t o r e d u c e t h e c o m p r e s s o r s t r o k e a n d
m a i n t a i n t h e r e q u i r e d e v a p o r a t o r p r e s s u r e .
T h e a u t o m a t i c c o n t r o l m e ch a n i s m c o m e s
f r o m t h e b e l l o w s w h i ch i s u n d e r p e r m a n e n t
v a c u u m o n i t s i n s i d e a n d e x p o s e d t o t h e
s u c t i o n p r e s s u r e o n t h e o u t s i d e . I f t h i s
p r e s s u r e d i ffe r e n t i a l f a l l s t o o l o w d u e t o
l o w s u c t i o n p r e s s u r e t h e b e l l o w s e x p a n d
t o d r i v e t h e n e e d l e t o o p e n t h e c o n n e c t i n g
p a s s a g e b e t w e e n d i s ch a r g e p r e s s u r e a n d
c r a n k c a s e . T h e r e s u l t i n g i n c r e a s e i n c r a n k
c a s e p r e s s u r e l e a d s t o a r e d u c t i o n i n s t r o k e
w i t h t h e c o n s e q u e n t i a l r e d u c t i o n i n r e f r i -
g e r a n t m a s s f l o w r a t e a n d i n c r e a s e i n s u c -
t i o n p r e s s u r e . A s t h e e v a p o r a t o r p r e s s u r e
i n c r e a s e s t h e p r e s s u r e d i ffe r e n t i a l d r i v e s
t h e n e e d l e t o c l o s e t h e c o n n e c t i n g p a s s a g e
b e t w e e n d i s ch a r g e p r e s s u r e a n d c r a n k c a s e .
T h e c r a n k c a s e p r e s s u r e f a l l s a s a r e s u l t o f
t h e s u c t i o n b l e e d a n d t h e c o m p r e s s o r s t r o k e
i n c r e a s e s .
0,4
0,3
0,2
0,1
0,0
Crank Case Pressure - bar
0 2 4 6 8 10 12 14 16
Swash-Plate Angle - radians
Compressor speed: 10 0 0 min-1
Suction pressure: 3 bar
Cur ves marked with head
pressure in bar.
9 12 15
Th e u s e o f ex t e r n a l c o n t r o l g i ve s a n ex t r a
d e g r e e o f f l ex i b i l i t y. P n e uma t i c c o n t r o l ma i n -
t a i n s eva p o r a t o r p r e s s u r e s o t h a t a i r- o ff
t e m p e r a t u r e s r e m a i n a fe w d e g r e e s a b o v e
0 ° C a n d a n y n e e d f o r h i g h e r t e m p e r a t u r e s
t h a n t h i s a r e a ch i e v e d b y m i x i n g w i t h w a r m
a m b i e n t o r r e c i r c u l a t e d a i r. A s a r e s u l t m o r e
c o m p r e s s o r w o r k i s d o n e t o c o o l t h e a i r
d o w n t o t h e l o w t e m p e r a t u r e t h a n i s r e a l l y
n e c e s s a r y. Ve r y s i g n i f i c a n t e n e r g y s a v i n g s
c a n b e m a d e b y u s i n g t h e e x t e r n a l c o n t r o l
t o m a n a g e t h e s y s t e m c a p a c i t y s o t h a t o n l y
s u ff i c i e n t c o o l i n g i s p r o v i d e d t o m e e t t h e
r e a l n e e d s o t h a t s i g n i f i c a n t r e h e a t i n g o f
t h e c o m f o r t a i r i s n o t n e e d e d .
T h i s p o t e n t i a l f o r e n e r g y s a v i n g i s t h e m o s t
i m p o r t a n t a s p e c t o f e x t e r n a l e l e c t r o n i c c o n -
t r o l b u t i t a l s o o f f e r s o t h e r a d v a n t a g e s s u c h
a s d e - s t r o k i n g a t s y s t e m s h u t d o w n s o t h a t
t h e e n g i n e l o a d f e l t b y t h e e n g i n e a t s y s t e m
s t a r t - u p c a n b e g r a d u a l l y i n c r e a s e d – k n o w n
a s “s o f t s t a r t ”. A f u r t h e r a d v a n t a g e i s t h e a b i l -
i t y t o e x e r c i s e a d e g r e e o f c o n t r o l o v e r c a b i n
h u m i d i t y a n d a v o i d e x c e s s i v e d r y n e s s t h a t
c a n o c c u r w i t h s i m p l e p n e u m a t i c c o n t r o l .
F i x e d c o m p r e s s o r s h a v e e l e c t r o m a g n e t i c a l l y
o p e r a t e d c l u t ch e s t o a l l o w s y s t e m c o n t r o l
b y s w i t ch i n g t h e c o m p r e s s o r d r i v e o n a n d
o ff a s r e q u i r e d . Va r i a b l e c o m p r e s s o r s h a v e
t r a d i t i o n a l l y r e t a i n e d t h e c l u t ch t o b e a b l e
t o t u r n t h e s y s t e m o ff w h e n n o t r e q u i r e d o r
s h o u l d s y s t e m c o n d i t i o n s a p p r o a ch u n s a fe
o p e r a t i n g l e v e l s f o r a n y r e a s o n . A m o r e r e c e n t
i n n o v a t i o n i s t h e i n t r o d u c t i o n o f c l u t ch l e s s
c o m p r e s s o r s . I t i s m a d e p o s s i b l e b y t h e
i m p l e m e n t a t i o n o f e x t e r n a l c o m p r e s s o r c o n -
t r o l . H e r e t h e c o m p r e s s o r c a n b e d e s t r o k e d
t o s u ch a n e x t e n t t h a t i t n o l o n g e r p u m p s
a n d c a n b e p e r m a n e n t l y d r i v e n w i t h o u t
d i s s i p a t i o n o f s i g n i f i c a n t e n e r g y. Ty p i c a l
d e s t r o k e d e n e r g y c o n s u m p t i o n i s o n l y 15 0W
a t 3 0 0 0 r e v / m i n . Ve r y s m a l l s t r o k e c a n b e
r e l a t i v e l y e a s i l y a ch i e v e d a n d t h e ch a l l e n g e
i s t o a c t i v a t e u p s t r o k e a g a i n w h e n r e q u i r e d .
T h e a d v a n t a g e s a r e p r i n c i p a l l y p a ck a g i n g
a n d w e i g h t a l t h o u g h c o s t s a v i n g s a r e a l s o
p o s s i b l e .
S e c t i o n t h r o u g h e l e c t r o n i c a l l y
c o n t r o l l e d c o m p r e s s o r v a l v e
SP - fixed displacement
## - displacement in cc/10
SP08
SP10
SP13
SP15
SP17
SP21
Fixed
Delphi engine-driven R134a compressor range
A Compressor Range
One frequently hears a need expressed with phrases such as: ”I want the most efficient and lightest component possible.” In reality however, it is not possible to optimise against two independent parameters at the same time - the most efficient possible will not necessarily be the lightest and vice-versa (other than by coincidence). While optimisation against a single parameter is possible, the significance of the second can only then be expressed as a limit or a constraint. “I want the most efficient component possible weighing less than 1kg.”
It is generally recognised that the automotive industry sources against the single optimisation parameter – cost. While there are very many other constraints within which they have to operate – both applications and market based constraints – these can only be expressed as limiting values. The target will always be to acquire the product that meets the needs of the application at the lowest possible cost. Since the needs expressed as constraints vary greatly, depending upon application, a supplier needs to offer an extensive range of compressors offering a spectrum of balances between sophistication and cost in order to stand a chance of meeting the needs of a significant proportion of the market. This will extend from simple fixed compressors to meet the most straightforward applications to electronically controlled variable compressors where performance, accuracy and efficiency play a more important role.
As means of illustration the Delphi compressor product range for R134a is indicated below. Compressors are shown with the trend for both increasing sophistication and cost going from left to right and increasing displacement going from top to bottom.
The SP range of fixed swash-plate compressors each with five double acting pistons represents the lowest cost solution for applications that can tolerate the implications of a cycling clutch. The double piston configuration means that in effect there are a total of ten compression cavities which yields very low levels of pressure fluctuation. This feature combined with the smoothness of the swash-plate drive results in an inherently quiet compressor.
The V5 range of wobble plate variable compressors has already been described as the original Delphi variable compressor. It has seen con-siderable refinement over the years and whilst it cannot compete with the CVC swash-plate range for quietness and efficiency it represents a very cost-effective introduction to variable compressor technology. The dual PTFE piston rings contribute to low blow-by and good oil retention.
The Compact Variable Compressor (CVC) range of compressors uses swash-plate technology to ensure that a/c system generated noise and vibration is kept to a minimum. Internally and externally controlled versions are available.
The externally controlled range of CVC compressors are offered with and without clutch. In the clutchless compressor the ability to upstroke again after destroke to a minimum that is only 1 or 2% of maximum stroke is ensured by the very tight tolerances of the piston and cylinder bore dimensions. They ensure very low blow-by which helps maintain low parasitic losses and ensure that upstroke can be achieved when required.
Variable
Wobble Plate
Increasing
displacement
Swash-Plate
Increasing sophistication and cost trend
### - displacement in cc
V - wobble plate
# - number of cylinders
i - internal control
e - external control
# - number of pistons
CVC - variable swash-plate
### - max displacement in cc
i - internal control
c - clutchless
e - external control
123V5i
132V5i
144V5i
151V5i
156V5i
156V5e
179V7e
5CVC120i
6CVC125i
6CVC135i
6CVC140i
6CVC160i
7CVC165i
7CVC185i
5CVC120c
6CVC125c
6CVC135c
6CVC140c
6CVC160c
7CVC165c
7CVC185c
5CVC120e
6CVC125e
6CVC135e
6CVC140e
6CVC160e
7CVC165e
7CVC185e
I t c a n b e s e e n t h a t t h e C VC r a n g e i s v e r y
c o m p r e h e n s i v e . N o t s h o w n h e r e i s t h e
f u r t h e r f l e x i b i l i t y o ffe r e d b y a v e r y w i d e
r a n g e o f p o s s i b l e p i p i n g c o n f i g u r a t i o n s
w h i ch t o g e t h e r c a r r y t h e i m p l i c a t i o n t h a t a
l a r g e n u m b e r o f d i ffe r e n t c o m p r e s s o r c o n -
f i g u r a t i o n s m u s t p a s s d o w n t h e p r o d u c t i o n
l i n e s . I t h a s b e e n c o n c l u d e d b y s o m e t h a t
t h i s c o m p l e x i t y i s l i k e l y t o h a v e a n e g a t i v e
e ffe c t o n p r o d u c t q u a l i t y w h e n i n f a c t t h e
o p p o s i t e i s t r u e . To m a n a g e t h e c o m p l e x i t y
a s y s t e m k n o w n a s R F I D – r a d i o f r e q u e n c y
i d e n t i f i c a t i o n – i s u s e d i n w h i ch e a ch i n d i v i d -
u a l c o m p r e s s o r c a r r i e s a ch i p w i t h i t d o w n
t h e p r o d u c t i o n l i n e . D u r i n g t h e p a s s a g e
d o w n t h e l i n e t h e ch i p r e a d s a n d v e r i f i e s a l l
t h e i n f o r m a t i o n a b o u t t h e i n d i v i d u a l c o m p o -
n e n t s a s t h e y a r e a s s e m b l e d ( m a n u f a c t u r i n g
d a t e s , d i m e n s i o n s , e t c ) a n d c o m m u n i c a t e s
i t b a ck t o a c e n t r a l c o m p u t e r f o r f i l i n g . T h i s
d a t a o n e a ch i n d i v i d u a l c o m p r e s s o r i s t h e n
a v a i l a b l e f o r l a t e r a c c e s s s h o u l d t h e r e b e
p r o b l e m s f u r t h e r d o w n t h e l i n e o r p r o b l e m s
f r o m t h e f i e l d . T h e a v a i l a b i l i t y o f a l l t h i s c o m -
p r e h e n s i v e a n d d e t a i l e d d a t a c o n t r i b u t e s t o
t h e e s t a b l i s h m e n t a n d m a i n t e n a n c e o f t h e
v e r y h i g h l e v e l s o f r e l i a b i l i t y r e q u i r e d b y t h e
a p p l i c a t i o n .
N e w T e c h n o l o g i e s
I n r e c e n t y e a r s a s e r i o u s i n t e r e s t i n t h e
u s e o f R 74 4 a s r e f r i g e r a n t i n a u t o m o t i v e
a i r c o n d i t i o n i n g s y s t e m s h a s b e e n g e n e -
r a t e d . E u r o p e a n l e g i s l a t i o n h a s r e c e n t l y
b e e n p a s s e d t h a t w i l l f o r c e t h e i n d u s t r y
t o m o v e a w a y f r o m R 13 4 a a n d R 74 4 h a s
b e c o m e t h e l e a d i n g c o n t e n d e r. A s a r e s u l t
D e l p h i i s d e v e l o p i n g a r a n g e o f s w a s h - p l a t e
c o m p r e s s o r s t o m e e t t h i s n e e d . C u r r e n t
p r o t o t y p e s h a v e f i v e p i s t o n s a n d m a x i m u m
d i s p l a c e m e n t o f 3 0 c c a l t h o u g h t h e n u m b e r
o f p i s t o n s i n t h e f i n a l p r o d u c t r a n g e i s s t i l l
u n d e r d e v e l o p m e n t . B o t h f i x e d a n d v a r i a b l e
v e r s i o n s o f d i s p l a c e m e n t s o f 15 , 2 1 a n d
3 0 c c a r e p l a n n e d . I t i s e n v i s a g e d t h a t f o r
l o w d i s p l a c e m e n t t h e n u m b e r o f p i s t o n s
w i l l b e b e t w e e n 5 a n d 7, a t t h e h i g h e n d i t
w i l l b e b e t w e e n 7 a n d 9 . T h e r e a s o n f o r t h i s
u n c e r t a i n t y i s t h a t t h e a p p r o p r i a t e b a l a n c e
b e t w e e n c o s t a n d n o i s e / d u r a b i l i t y h a s n o t
y e t b e e n e s t a b l i s h e d .
I t c a n b e s e e n t h a t a s a r e s u l t o f t h e v e r y
d i ffe r e n t f l u i d p r o p e r t i e s , t h e d i s p l a c e m e n t s
o ffe r e d a r e v e r y m u ch l o w e r t h a n f o r R 13 4 a .
T h e r a n g e fe a t u r e s s h a ft s e a l i n g b y f a c e s e a l
a n d i n t e r n a l o i l s e p a r a t o r. T h e n e e d f o r t h e
l a tt e r c o m e s f r o m t h e s i g n i f i c a n t e v a p o r a t o r
p e r f o r m a n c e d e g r a d a t i o n t h a t o c c u r s w i t h
C O 2 i f e x c e s s o i l i s a l l o w e d t o c i r c u l a t e .
T h e s e c o n d n e w t e ch n o l o g y c o n c e r n s c o m -
p r e s s o r s f o r f u t u r e p o w e r t r a i n s , w h e t h e r
h y b r i d o r f u e l c e l l – t h e e l e c t r i c a l l y d r i v e n
c o m p r e s s o r. U n d e r d e v e l o p m e n t i s a f a m i l y
o f s c r o l l c o m p r e s s o r s d r i v e n b y 3 15 v o l t
b r u s h l e s s e l e c t r i c m o t o r s . S c r o l l d i s p l a c e -
m e n t s a r e 2 8 a n d 3 8 c c f o r c o o l i n g c a p a c i t i e s
o f 5 . 6 a n d 7. 1 kW r e s p e c t i v e l y. T h e m o t o r s
a r e c o o l e d u s i n g t h e l o w t e m p e r a t u r e r e -
f r i g e r a n t v a p o u r f r o m t h e e v a p o r a t o r w i t h
a r e s u l t a n t m o t o r e ff i c i e n c y o f 9 4% . T h e
i n v e r t e r i s c o o l e d b y c o n d u c t i o n f r o m t h e
s a m e r e f r i g e r a n t a n d i t t o o h a s e ff i c i e n c y i n
t h e 9 4 t o 9 8% r a n g e .
D e l p h i C O 2 c o m p r e s s o r
S e c t i o n t h r o u g h D e l p h i E l e c t r i c C o m p r e s s o r
1 S c r o l l C o m p r e s s o r
2 Pe r m a n e n t M a g n e t M o t o r
3 I n v e r t e r a n d I n t e g r a t e d E l e c t r o n i c s
1 2
3
C o n c l u s i o n
T h i s p a p e r h a s a ime d to p re s e n t t h e te ch n i c a l re q u i reme n t s o f t h e c omp re s s o r fo r u s e i n
a u tomo t i ve a i r c o n d i t i o n i n g a p p l i c a t i o n s a n d to s h ow h ow t h e d i ve r s e re q u i reme n t s o f t h e
a p p l i c a t i o n me a n t h a t a s u p p l i e r mu s t h ave ava i l a b l e a ra n ge o f te ch n o l o g i e s a n d s p e c i f i -
c a t i o n s to b e a b l e to me e t t h e s e n e e d s . I t go e s o n to s h ow h ow t h e D e l p h i c omp re s s o r
p ro d u c t ra n ge i s d e s i g n e d to g i ve c omp re h e n s i ve c ove ra ge a n d f i n i s h e s wi t h c o n s i d e ra t i o n
o f c omp re s s o r s fo r d e ve l o pme n t a l te ch n o l o g i e s t h a t a re l i ke l y to b e c ome s i g n i f i c a n t i n t h e
re l a t i ve l y n e a r f u tu re .
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p e r a t u r e , q u a l i t y a n d m o v e m e n t i n a l l c o r n e r s
o f t h e v e h i c l e . T h e m o d e r n h e a t i n g , v e n t i l a -
t i n g a n d a i r c o n d i t i o n i n g s y s t e m ( H VAC ) c a n
e n s u r e t h a t t h e r m a l c o m f o r t a n d a l l r o u n d
v i s i b i l i t y a r e d e l i v e r e d i n e n v i r o n m e n t s t h a t
r a n g e f r o m t h e h e a t o f P h o e n i x A r i z o n a t o
t h e c o l d e s t S c a n d i n a v i a n w i n t e r.
I n t r o d u c t i o n
T h e p a s s e n g e r c o m p a r t m e n t o f a m o d e r n
a u t o m o b i l e o ffe r s a v e r y d i ffe r e n t e n v i r o n -
m e n t t o t h a t o f a v e h i c l e f r o m f i ft y y e a r s
a g o . A s w e l l a s t h e e r g o n o m i c a l l y d e s i g n e d
s e a t i n g a n d i n s t r u m e n t l a y o u t , t h e a l l r o u n d
v i s i b i l i t y a n d t h e e ff i c i e n t u s e o f s p a c e ,
t o d a y ’s p a s s e n g e r h a s c o n t r o l o v e r a i r t e m -
V i e w o f i n s t r u m e n t p a n e l a n d H VAC c o n t r o l s
E x p a n d e d v i e w o f a m o d e r n
H VAC c o m p r e s s o r
T h e v e r y h e a r t o f t h e a i r c o n d i t i o n i n g s y s -
t e m i s t h e c o m p r e s s o r. I t s k e y t a s k s a r e t o
g e n e r a t e t h e r e q u i r e d f l o w o f r e f r i g e r a n t
a r o u n d t h e s y s t e m a n d a t t h e s a m e t i m e
t o c o m p r e s s i t s u ff i c i e n t l y t o r a i s e i t s
t e m p e r a t u r e a b o v e t h e a m b i e n t i n o r d e r
t h a t h e a t c a n b e r e j e c t e d f r o m t h e s y s t e m .
T h e s e d e m a n d s m u s t b e m e t e ff i c i e n t l y o v e r
v e r y w i d e r a n g e s o f c o m p r e s s o r s p e e d a n d
a m b i e n t c o n d i t i o n s . A t t h e s a m e t i m e v e r y
d e m a n d i n g n o i s e g e n e r a t i o n c o n s t r a i n t s a n d
e x p e c t a t i o n s o f d u r a b i l i t y h a v e t o b e m e t .
A i r C o n d i t i o n i n g
C y c l e
I t i s s e l f e v i d e n t t h a t h e a t t e n d s t o f l o w
f r o m h i g h t e m p e r a t u r e t o l o w. I f w e w i s h t o
p r o v i d e c o o l i n g a t a l o c a t i o n i n a h i g h t e m p e -
r a t u r e e n v i r o n m e n t t h e n w e a r e e ffe c t i v e l y
a s k i n g h e a t t o f l o w f r o m l o w t e m p e r a t u r e
t o h i g h . To a ch i e v e t h i s i t i s n e c e s s a r y t o
o p e r a t e a t h e r m o d y n a m i c c y c l e i n w h i ch a
r e f r i g e r a n t a t a l o w t e m p e r a t u r e i s u s e d t o
e x t r a c t h e a t f r o m t h e l o c a t i o n t o b e c o o l e d .
T h e r e f r i g e r a n t i s s u b s e q u e n t l y c o m p r e s s e d
u n t i l i t b e c o m e s h o t e n o u g h t o b e a b l e t o
r e j e c t h e a t t o t h e a m b i e n t . A ft e r c o o l i n g t o
n e a r a m b i e n t t e m p e r a t u r e b y t h e a m b i e n t
a i r, i t i s e x p a n d e d b a ck t o l o w p r e s s u r e , a
p r o c e s s w h i ch g e n e r a t e s f u r t h e r r e f r i g e r a n t
t e m p e r a t u r e r e d u c t i o n t h a t b e c o m e s l o w
e n o u g h t o b e u s e d f o r c o o l i n g a t t h e r e -
q u i r e d l o c a t i o n . T h e c y c l e i s c o m p l e t e . T h e
required cooling is thus achieved but at the expense of the work necessary to drive the compressor.
The Automotive
Air Conditioning
Application
The automotive application places very special demands on the air conditioning system. A typical vehicle system has a similar cooling capacity to that required for the air conditioning of a small house despite the vast difference in volumes to be cooled. The reasons for this are twofold. Firstly cooling duty per unit volume is much higher for the vehicle because heat transfer coefficients between hot ambient air and the outside surfaces are much higher due to movement of the vehicle through the air. Secondly the proportion of the enclosure consisting of glass is very high for the vehicle – a factor that makes the effect of direct solar radiation heating very high. On top of this a particularly demanding requirement is to cool the cabin very rapidly after the vehicle has been soaked in an ambient temperature of 40°C or higher. At the start of the cool down temperatures in the cabin can be as high as 60 or 70°C.
Another significant way in which automotive air conditioning differs from the domestic or commercial version is the question of compressor drive. In the vehicle the compressor is belt driven by the engine so that independent control over the compressor speed is not possible. This obviously has significant implications for system control and means that there can be calls for high system performance at times when the compressor speed is very low. An important
The challenge of compressor packaging
implication of this is that the compressor drive shaft must pass out of the compressor casing with the resultant potential for refrigerant leakage. Hermetic compressors are not possible and very effective shaft seals must be used. A second implication of the external drive is that the compressor must be engine mounted so that lengths of flexible hose must be introduced to accommodate relative movement between engine and chassis mounted components.
As with other air conditioning applications system efficiency is very important and the
automotive application is no exception. While
the characteristics of all the major components in the system contribute to overall efficiency any compressor inefficiencies must be kept to a minimum. A further feature of the compressor that requires serious consideration is its intrinsic noise generation - modern vehicle noise requirements mean that the compressor must be very quiet and vibration free.
And finally, three further requirements of the compressor, specific to the automotive application, but which apply equally to every vehicle component – are stringent con-straints on size, weight and cost.
As a result of all these constraints deriving from the use of an engine driven compressor, it is often suggested that an electrically driven system would provide a much better solution. The reason that it is not feasible on current vehicles is insufficient electrical power is available and its application must await the widespread implementation of high
powered and efficient integrated starter/
generators. The applications in which an electrical compressor would make real sense however are in hybrid and fuel cell vehicles where sufficient electrical power is readily available.
h
eat rejected to ambientexpansion deviceheat absorbed from cabincondenserevaporatorcompressor
Schematic of air conditioning cycle
D e l p h i v e h i c l e w i t h H e a t P u m p s u p p l e m e n t a r y h e a t i n g
T h e h i g h e ff i c i e n c y o f m o d e r n e n g i n e s c a n
l e a d t o t h e s i t u a t i o n i n w h i ch i n s u ff i c i e n t r e -
j e c t e d h e a t i s a v a i l a b l e f o r c o m f o r t h e a t i n g .
T h i s f a c t h a s p r o m p t e d t h e s u g g e s t i o n t h a t
t h e a i r c o n d i t i o n i n g s y s t e m b e o p e r a t e d i n
r e v e r s e a s a h e a t p u m p t o s u p p l e m e n t t h e
e n g i n e h e a t a n d t h e v i a b i l i t y o f t h e c o n c e p t
h a s b e e n d e m o n s t r a t e d o n a n u m b e r o f p l a t -
f o r m s . T h e i m p l i c a t i o n s f o r t h e c o m p r e s s o r
a r e t h a t t h e r e q u i r e d o p e r a t i n g l i fe c a n b e
n e a r l y d o u b l e d a n d t h e c o m p r e s s o r a m b i e n t
s a fe o p e r a t i n g t e m p e r a t u r e r a n g e m u s t b e
e x t e n d e d d o w n w a r d s t o m i n u s 2 0 ° C .
R e f r i g e r a n t I s s u e s
T h e a u t o m o t i v e a i r c o n d i t i o n i n g i n d u s t r y
r e s p o n d e d p r o - a c t i v e l y t o t h e d e m a n d s o f
t h e 19 8 7 M o n t r e a l P r o t o c o l a n d b y 19 9 4 ,
2 y e a r s e a r l y, t h e ch a n g e o v e r f r o m R 12 t o
R 13 4 a w a s c o m p l e t e f o r a l l v e h i c l e p r o d u c -
t i o n l i n e s i n t h e d e v e l o p e d w o r l d . I t s o o n
b e c a m e a p p a r e n t t h a t t h i s m a y n o t b e t h e
e n d o f t h e s t o r y a n d w i t h i n c r e a s i n g p e n e -
t r a t i o n o f a i r c o n d i t i o n i n g i n t h e E u r o p e a n
m a r k e t t o g e t h e r w i t h t h e d e m a n d s o f t h e
Ky o t o P r o t o c o l p r e s s u r e h a s b u i l t t o m a k e
ch a n g e s t o s t i l l f u r t h e r r e d u c e t h e p o t e n t i a l
c o n t r i b u t i o n o f a i r c o n d i t i o n i n g s y s t e m s
t o g l o b a l w a r m i n g . A n e w D i r e c t i v e h a s
r e c e n t l y c o m p l e t e d i t s p r o g r e s s t h r o u g h t h e
E u r o p e a n l e g i s l a t i v e p r o c e s s . I t r e q u i r e s t h e
e l i m i n a t i o n o f R 13 4 a f r o m a l l n e w m o d e l s
f r o m 2 011 a n d f r o m a l l n e w v e h i c l e s b y 2 017.
T h e c u r r e n t l y c o n s i d e r e d a l t e r n a t i v e s a r e
R 15 2 a w i t h a g l o b a l w a r m i n g p o t e n t i a l l e s s
t h a n 10 % o f t h a t o f R 13 4 a , o r t h e s o - c a l l e d
‘ n a t u r a l ’ r e f r i g e r a n t R 74 4 ( c a r b o n d i o x i d e ) .
R 15 2 a h a s t h e r m o d y n a m i c ch a r a c t e r i s t i c s
v e r y s i m i l a r t o t h o s e o f R 13 4 a a n d w i l l b e
d i r e c t l y u s a b l e w i t h c u r r e n t c o m p r e s s o r
t e ch n o l o g y. I t s p o t e n t i a l d r a w b a ck i s a
d e g r e e o f f l a m m a b i l i t y t h a t h a s m a d e t h e
i n d u s t r y r e l u c t a n t t o c o n s i d e r i t . M o r e r e -
c e n t l y o t h e r l a r g e ch e m i c a l c o m p a n i e s h a v e
a n n o u n c e d t h e p o t e n t i a l a v a i l a b i l i t y o f n e w
a l t e r n a t i v e s . L i tt l e i s k n o w n a b o u t t h e m a t
t h i s s t a g e b u t i t i s a s s u m e d t h a t t h e y t o o
w o u l d f u n c t i o n w i t h c u r r e n t c o m p r e s s o r
t e ch n o l o g y. T h e r e m u s t b e a q u e s t i o n a s t o
w h e t h e r t h e n e c e s s a r y d e v e l o p m e n t a n d
100 200 300 400 500 600 700
1
10
100
Enthalpy - kJ/kg
Pressure - MPa
-40°C
0°C
40°C
80°C 120°C 160°C 200°C
200°C
160°C
120°C
80°C
40°C
0°C
I d e a l i z e d p r e s s u r e e n t h a l p y d i a g r a m o f C O 2 c y c l e
t e s t i n g a n d t h e n i m p l e m e n t a t i o n o f t h e
n e c e s s a r y m a n u f a c t u r i n g c a p a c i t y c a n b e
c o m p l e t e d i n t i m e t o m e e t t h e r e q u i r e m e n t s
o f t h e E u r o p e a n l e g i s l a t i o n . I f R 74 4 b e c o m e s
t h e ch o s e n r o u t e t h e i m p l i c a t i o n s f o r c o m -
p r e s s o r t e ch n o l o g y a r e v e r y f a r- r e a ch i n g . A i r
c o n d i t i o n i n g s y s t e m s w i t h R 74 4 n e e d c o m -
p r e s s o r s w i t h d i s p l a c e m e n t o f o n l y a f i ft h
o f t h a t r e q u i r e d f o r R 13 4 a b u t o p e r a t i n g a t
mu ch h i g h e r p r e s s u r e s . D i s ch a r g e p r e s s u r e s
o f 12 0 b a r a r e n o rma l c omp a r e d w i t h a t y p i -
c a l 18 b a r f o r a n R 13 4 a s y s t em. A s c a n b e
ima g i n e d , t h e s e f a c t o r s h a v e b i g imp l i c a t i o n s
f o r t h e c omp r e s s o r l a y o u t a n d s t ru c tu r a l
s t r e n g t h r e q u i r eme n t s a n d a l s o r e p r e s e n t a
p a r t i c u l a r l y s e v e r e s h a ft s e a l ch a l l e n g e .
A n e a r l y
c o m p r e s s o r,
t h e D e l p h i R 4
C o m p r e s s o r
T e c h n o l o g i e s
A i r c o n d i t i o n i n g b e g a n t o b e c o m e a v a i l a b l e
f o r v e h i c l e s i n t h e e a r l y 19 5 0 s . Fr o m t h e
b e g i n n i n g a n u m b e r o f d i ffe r e n t c o m p r e s s o r
t e ch n o l o g i e s h a v e b e e n u s e d . T h e e a r l i e s t
s y s t e m s u s e d p i s t o n c o m p r e s s o r s i n v a r i o u s
c o n f i g u r a t i o n s . T h e Fr i g i d a i r e F 5 , a f i v e p i s -
t o n w o b b l e p l a t e c o n f i g u r a t i o n , u s e d i n t h e
e a r l i e s t G M v e h i c l e s w i t h a i r c o n d i t i o n i n g
w a s f i r s t p r o d u c e d i n 19 5 6 – i t w e i g h e d i n a t
1 8 k g ! T h e R 4 c o m p r e s s o r w i t h a s c o t ch y o k e
m e ch a n i s m w a s f i r s t p r o d u c e d b y H a r r i s o n
( n o w D e l p h i ) i n 19 74 a n d r e m a i n e d i n p r o -
d u c t i o n u n t i l 19 9 5 . I t w a s 19 0 m m i n o v e r a l l
d i a m e t e r a n d w e i g h e d 9 k g .
S e c t i o n t h r o u g h a n e a r l y f i x e d s w a s h - p l a t e
c o m p r e s s o r, t h e D e l p h i H D 6
I l l u s t r a t i o n o f S c r o l l c o m p r e s s i o n p r o c e s s
T h e m e ch a n i s m o f a v a r i a b l e w o b b l e p l a t e c o m p r e s s o r
T h e p r e fe r r e d c o n f i g u r a t i o n f o r a p i s t o n
c o m p r e s s o r s o o n m o v e d t o a d o u b l e a c t i n g
s w a s h - p l a t e d e s i g n o f w h i ch t h e H a r r i s o n
( D e l p h i ) H D 6 i s t y p i c a l . T h e f i x e d s w a s h -
p l a t e i s h e l d b e t w e e n t h e o p p o s i n g e n d s
o f t h e d o u b l e p i s t o n b y a p a i r o f s h o e s a n d
t w o s t e e l b a l l s .
A s e c o n d p o s i t i v e d i s p l a c e m e n t c o n f i g u r a -
t i o n u s e d i s t h e s l i d i n g v a n e . I t o ffe r s a d -
v a n t a g e s o f c o m p a c t n e s s a n d l o w c o s t b u t
c a r r i e s t h e p e n a l t y o f v e r y p o o r e ff i c i e n c y a t
h i g h p r e s s u r e r a t i o s .
T h e o t h e r m a i n c o n f i g u r a t i o n i s t h e s c r o l l
c o m p r e s s o r i n w h i ch o n e s c r o l l w i t h a n i n -
v o l u t e s u r f a c e o r b i t s i n s i d e a f i x e d s e c o n d
s c r o l l o f t h e s a m e s h a p e . I t c a n b e s e e n
f r o m t h e f i g u r e t h a t t h e c o n t a c t p o i n t s o f
t h e s c r o l l s e n c l o s e a c a v i t y o f r e d u c i n g s i z e
( s h a d e d g r e e n ) t h a t m o v e s f r o m t h e o u t s i d e
t o t h e c e n t r e a s t h e o n e s c r o l l o r b i t s i n s i d e
t h e o t h e r. T h e r e s u l t i s a n i n d u c t i o n o f g a s
a t t h e p e r i p h e r y o f t h e s c r o l l a n d d e l i v e r y
o f c o m p r e s s e d g a s a t t h e c e n t r e . T h e s e
c o m p r e s s o r s a r e v e r y e ff i c i e n t a n d q u i e t
b u t r e p r e s e n t a s i g n i f i c a n t ch a l l e n g e f o r
m a n u f a c t u r e a n d h e n c e f o r c o s t . T h e y h a v e
t h e d i s a d v a n t a g e t h a t a l t h o u g h a v a r i a b l e
v e r s i o n o f t h i s c o m p r e s s o r i s p o s s i b l e , t h e
s u p e r i o r e ff i c i e n c y a d v a n t a g e i s l o s t .
E a r l y c o m p r e s s o r s w e r e a l l f i x e d d i s p l a c e -
m e n t a n d s y s t e m c o n t r o l w a s a ch i e v e d b y
s w i t ch i n g t h e c o m p r e s s o r o n a n d o ff b y
m e a n s o f a n e l e c t r o - m e ch a n i c a l c l u t ch
c o n t a i n e d w i t h i n t h e c o m p r e s s o r p u l l e y.
A s c o n s i d e r a t i o n b e g a n t o b e g i v e n t o t h e
a p p l i c a t i o n o f a i r c o n d i t i o n i n g t o s m a l l e r
v e h i c l e s w i t h s m a l l e r e n g i n e s i t w a s f o u n d
t h a t t h e s i g n i f i c a n t a n d s u d d e n i n c r e a s e i n
e n g i n e l o a d t h a t r e s u l t e d f r o m c o m p r e s s o r
s w i t ch i n g c a u s e d p r o b l e m s f o r t h e s m a l l
e n g i n e w i t h r e s u l t a n t i s s u e s o f d r i v a b i l i t y.
A c o m p r e s s o r w i t h v a r i a b l e d i s p l a c e m e n t
o ffe r e d t h e s o l u t i o n t o t h i s p r o b l e m . I n 19 8 5
H a r r i s o n ( D e l p h i ) w e r e t h e f i r s t t o g o i n t o
s e r i e s p r o d u c t i o n w i t h a v a r i a b l e c o m p r e s -
s o r, t h e V 5 , a w o b b l e p l a t e d e s i g n w i t h f i v e
p i s t o n s .
A l t h o u g h s c r o l l , v a n e a n d p i s t o n c o m p r e s -
s o r s a r e a l l s t i l l i n u s e i n a u t o m o t i v e a p p l i c a -
t i o n s , t h e p i s t o n c o m p r e s s o r i s d o m i n a n t .
W h e r e t h e c o m b i n a t i o n o f e ff i c i e n c y a n d
c o n t r o l l a b i l i t y i s t h e k e y r e q u i r e m e n t , p i s t o n
c o m p r e s s o r s o ffe r t h e b e s t s o l u t i o n .
P i s t o n C o m p r e s s o r s
T h e c o m p r e s s o r h a s t h e t a s k o f i n d u c i n g g a s
a t a l o w s u c t i o n p r e s s u r e a n d d e l i v e r i n g i t a t
a h i g h e r d i s ch a r g e p r e s s u r e . I t a ch i e v e s t h i s
b y u s i n g r e e d v a l v e s t h a t o p e r a t e a u t o m a -
t i c a l l y t o c o n t r o l t h e f l u i d f l o w i n t o a n d o u t o f
t h e c y l i n d e r s . S t a r t i n g w i t h t h e p i s t o n a t t o p
d e a d c e n t r e t h e p r e s s u r e i n t h e s m a l l c l e a ra
n c e v o l u m e w i l l b e c l o s e t o t h e d i s ch a r g e
p r e s s u r e a s t h e p i s t o n h a s j u s t d e l i v e r e d i t s
ch a r g e . A s t h e p i s t o n r e c e d e s a n d t h e p r e s -
s u r e i n t h e c l e a r a n c e v o l u m e f a l l s , t h e d e l i v e -
r y r e e d v a l v e c l o s e s a u t o m a t i c a l l y, d r i v e n b y
t h e d i s ch a r g e p r e s s u r e . S i n c e t h e c l e a r a n c e
C
ylinder volume - cm3discharge pressure Pdsuction pressure Ps05101520251051520Cylinder Pressure -
bar
Indicator diagram for swash-plate compressor
volume is small, the pressure drops quickly
until it is below the suction pressure. At this stage the intake valve opens and the further movement of the piston induces fresh charge.
After bottom dead centre the piston compresses the gas induced into the cylinder until it reaches the discharge pressure. At this stage the delivery valve is opened automatically by the pressure differential and the compressed charge is delivered.
There are several key features of this overall process important for performance and efficiency. The clearance volume must be as
small as possible without risking interference between the piston and the cylinder head as a result of differential thermal expan-sion or stress effects. The consequences of finite clearance volume are principally indicated by the compressor volumetric efficiency which is the ratio of the volume of delivered gas measured at the suction pressure relative to volume displaced by the
piston. The dynamic response characteristics of the reed valves are also important. Volumetric efficiency is also impacted by the quantity of gas that leaks past the pistons to the crank case, which is determined by piston sealing and clearances.
Efficiency Definition
volumetric ηv delivered volume
displaced volume
ideal minimum work needed
isentropic ηs work done to compress gas
work done on compressed gas
mechanical ηm work input to compressor shaft
Table of compressor efficiencies
The second measure of compressor performance quality is the isentropic efficiency. It is given by the ratio of the theoretical minimum work required to compress the gas from suction to discharge pressure relative to the work actually done. The theoretical minimum is based on an idealized ‘isentropic’ process in which no turbulence genera-tion or viscosity effects occur. The third measure of compressor performance quality is the mechanical efficiency. This is the ratio of the work actually done on the gas relative to the measured power input to the compressor shaft. The difference between these two figures is due to friction.
Variable Piston
Compressors
As stated above, Harrison (now Delphi) was the first to go into series production with a variable compressor. The wobble plate that drives the pistons with this design is free to tilt so that the piston stroke, and hence displacement can be changed. The wobble plate mechanism allows very short and compact pistons to be used. The ball-ended connecting rods are swaged into the pistons and wobble plate which results in strong, low friction and very simple joints. The fact that the connecting rods are tilted slightly during compression as a result of the wobble plate movement means that the forces act-ing do not all lie along the piston axes. The result is that higher vibrational harmonics can be generated which makes management of compressor noise more of a challenge than with later generations of swash-plate compressor. Nonetheless the value of this configuration is illustrated by the fact that it is still produced at a rate of several million units per year worldwide for installation in new vehicles as original equipment, offering a good compromise between cost and the functionality of a variable displacement com-pressor.
The next generation of variable compressors used a swash-plate mechanism, largely because of its advantages of low vibration and noise. The mechanism by which the compressor displacement is controlled can be described in principle relatively simply, but in fact the actual displacement of the compressor in any given situation results from a quite complex interaction of forces.
Va r i a b l e s w a s h - p l a t e c o m p r e s s o r s h o w i n g m e ch a n i s m
Ta b l e o f s w a s h - p l a t e t o r q u e g e n e r a t i n g m e ch a n i s m s
T h e s w a s h - p l a t e h a s a l i n k a g e m e ch a n i s m
t h a t a l l o w s i t t o r o t a t e t h u s ch a n g i n g i t s a n -
g l e a n d w i t h i t , t h e p i s t o n d i s p l a c e m e n t . T h e
l i n k a g e i s d e s i g n e d s o t h a t t h e c l e a r a n c e
v o l u m e r e m a i n s a s c o n s t a n t a n d s m a l l a s
p o s s i b l e o v e r t h e f u l l s w a s h - p l a t e a n g l e
r a n g e f r o m f u l l s t r o k e t o m i n i m u m s t r o k e .
T h i s s w a s h - p l a t e s f r e e d o m t o r o t a t e m e a n s
t h a t u n d e r a n y g i v e n o p e r a t i n g c o n d i t i o n s
i t w i l l t a k e u p a p o s i t i o n t h a t i s d e t e r m i -
n e d b y t h e b a l a n c e o f a l l t h e f o r c e s a c t i n g
o n i t t h a t t e n d t o c a u s e i t t o r o t a t e a b o u t
i t s c e n t r e o f r o t a t i o n . T h e f i r s t e l e m e n t o f
c o m p l e x i t y i s t h a t t h e c e n t r e o f r o t a t i o n i s
n o t f i x e d a s i t s h i ft s l o c a t i o n s l i g h t l y w i t h
t h e s w a s h - p l a t e a n g l e . I t l i e s f a i r l y n e a r t o
t h e s w a s h - p l a t e c o n n e c t i o n w i t h t h e l i n k b u t
i t s e x a c t l o c u s i s a f u n c t i o n o f t h e l i n k a g e
m e ch a n i s m l o c a t i o n , d i m e n s i o n s a n d o f t h e
s w a s h - p l a t e a n g l e . T h e m o s t o b v i o u s f o r c e
t h a t c o m e s i n t o p l a y i s t h e g a s p r e s s u r e
a c t i n g o n t h e p i s t o n c r o w n . E s t i m a t i o n o f
i t s a v e r a g e e ffe c t , h o w e v e r i s c o m p l e x a s
t h e c y l i n d e r p r e s s u r e v a r i e s g r e a t l y a r o u n d
t h e c y c l e . A t t h e s a m e t i m e i t s l i n e o f a c t i o n
i s c o n t i n u a l l y ch a n g i n g a n d h e n c e s o i s t h e
e ffe c t i v e t o r q u e i t e x e r t s a b o u t t h e c e n t r e
o f r o t a t i o n . T h i s t o r q u e w i l l o b v i o u s l y t e n d
t o u p s t r o k e t h e c o m p r e s s o r.
A l e s s o b v i o u s s o u r c e o f t o r q u e g e n e r a t i o n
o n t h e s w a s h - p l a t e i s t h e i n e r t i a o f t h e p i s -
t o n s w h i ch a r e r e p e a t e d l y a c c e l e r a t e d a n d
d e c e l e r a t e d a s t h e c o m p r e s s o r i s o p e r a t e d .
I t m i g h t b e t h o u g h t t h a t t h e e ffe c t o f t h e
f o r c e s f o r a c c e l e r a t i o n a n d d e c e l e r a t i o n
c a n c e l e a ch o t h e r o u t b u t i n f a c t t h e p i s t o n
i s a c c e l e r a t e d u p w a r d s o v e r t h e h a l f o f t h e
s w a s h - p l a t e f u r t h e s t f r o m i t s c e n t r e o f r o t a -
t i o n a n d c o r r e s p o n d i n g l y d e c e l e r a t e d o v e r
t h e h a l f n e a r e s t t o t h e c e n t r e o f r o t a t i o n .
T h e f o r m e r t h e r e f o r e e x e r t s g r e a t e r t o r q u e
a n d t h e n e t r e s u l t i s a t e n d e n c y t o u p s t r o k e
w h i ch i s p r o p o r t i o n a l t o t h e s q u a r e o f t h e
p i s t o n s p e e d a n d t h u s b e c o m e s s i g n i f i c a n t
a t h i g h e r c o m p r e s s o r s p e e d s .
A s e c o n d t o r q u e g e n e r a t i n g f o r c e t h a t i s a
s i m i l a r f u n c t i o n o f c o m p r e s s o r s p e e d c o m e s
f r o m c e n t r i f u g a l a ffe c t s a c t i n g o n b o t h t h e
l i n k m e ch a n i s m a n d t h e s w a s h - p l a t e i t s e l f. I f
o n e c o n s i d e r s t h e t w o h a l v e s o f t h e s w a s h -
p l a t e n e a r e s t a n d m o s t r e m o t e f r o m t h e c e n -
t r e o f r o t a t i o n i t i s c l e a r t h a t t h e c e n t r i f u g a l
f o r c e s o f t h e m o r e r e m o t e h a l f g e n e r a t e t h e
g r e a t e r t o r q u e a n d t h e n e t r e s u l t w i l l b e a
t e n d e n c y t o d e s t r o k e t h e c o m p r e s s o r.
Fu r t h e r f o r c e s g e n e r a t i n g r o t a t i o n t o r q u e
c a n c o m e f r o m t h e f i tt i n g o f u p s t r o k e a n d / o r
d o w n s t r o k e s p r i n g s . T h e s e c a n b e i n s t a l l e d
o n t h e s h a ft t o a s s i s t t h e u p s t r o k e / d o w n -
s t r o ke p r o c e s s u n d e r s ome c omp r e s s o r o p e r a -
t i n g c o n d i t i o n s a n d i f f i tt e d w i l l o b v i o u s l y
c o n t r i b u t e t o t h e o v e r a l l b a l a n c e o f t o r q u e s .
H e r e t h e e ffe c t w i l l b e a s i m p l e f u n c t i o n o f
t h e s w a s h - p l a t e a n g l e .
T h e f i n a l c o n t r i b u t o r t o t h e b a l a n c e o f t o rq
u e s i s t h a t g e n e r a t e d o n t h e u n d e r s i d e
o f t h e p i s t o n s b y t h e c r a n k c a s e p r e s s u r e .
A l t h o u g h t h e c r a n k c a s e p r e s s u r e r e m a i n s
c o n s t a n t a r o u n d t h e c y c l e i t s l i n e o f a c t i o n
a r o u n d t h e p l a t e m u s t b e i n t e g r a t e d t o o b -
t a i n a n a v e r a g e n e t t o r q u e . I t i s t h e a b i l i t y t o
c o n t r o l t h i s p r e s s u r e t h a t a l l o w s t h e b a l a n c e
t o b e s h i ft e d a n d t h u s t h e s w a s h - p l a t e a n g l e
t o b e c o n t r o l l e d . C r a n k c a s e p r e s s u r e i s c o n -
t r o l l e d w i t h b l e e d s f r o m b o t h s u c t i o n a n d
h i g h s i d e . T h e s m a l l s u c t i o n b l e e d i s u s u a l l y
p e r m a n e n t a n d t h e h i g h s i d e b l e e d i s c o n -
t r o l l e d b y m e a n s o f a v a l v e . I f t h e h i g h s i d e
b l e e d i s c l o s e d t h e s u c t i o n b l e e d p u m p s t h e
c r a n k c a s e d o w n t o s u c t i o n p r e s s u r e w i t h t h e
r e s u l t t h a t t h e c o m p r e s s o r o p e r a t e s a t f u l l
M e c h a n i s m E f fe c t C o m m e n t
C y l i n d e r p r e s s u r e U p s t r o k e I n t e g r a t e d a r o u n d s w a s h - p l a t e
P i s t o n i n e r t i a U p s t r o k e S i g n i f i c a n t a t h i g h s p e e d
C e n t r i f u g a l f o r c e s D e s t r o k e S i g n i f i c a n t a t h i g h s p e e d
S p r i n g s U p s t r o k e / d e s t r o k e W h e r e f i tt e d
C r a n k c a s e p r e s s u r e D e s t r o k e A d j u s t e d f o r c o n t r o l
C o m p r e s s o r c o n t r o l c u r v e s
S e c t i o n t h r o u g h
p n e u m a t i c c o m p r e s s o r
c o n t r o l v a l v e
s t r o k e . I f t h e d i s ch a r g e p r e s s u r e g e t s t o o
h i g h , t h e h i g h p r e s s u r e b l e e d c a n b e o p e n e d
a n d t h e c r a n k c a s e p r e s s u r e i n c r e a s e s . A t
s o m e s t a g e i t w i l l b e h i g h e n o u g h f o r t h e
b a l a n c e o f t o r q u e s t o d e s t r o k e t h e c o m p r e s -
s o r. T h e c o n t r o l h a s b e e n a ch i e v e d .
T h e h i g h p r e s s u r e c o n t r o l v a l v e c a n b e a n
a u t o m a t i c , s p r i n g o p e r a t e d v a l v e o r a n e l e c -
t r i c a l l y s w i t ch e d a n d e l e c t r o n i c a l l y c o n t r o l -
l e d v a l v e . T h e f o r m e r c o n f i g u r a t i o n i s k n o w n
a s p n e u m a t i c c o n t r o l , t h e l a tt e r i s c a l l e d
e x t e r n a l c o n t r o l .
T h e d o m i n a n t e l e m e n t o f s y s t e m c o n t r o l
i s t h e t h e r m a l e x p a n s i o n v a l v e t h a t a c t s t o
m a i n t a i n a g i v e n d e g r e e o f s u p e r h e a t o f t h e
r e f r i g e r a n t l e a v i n g t h e e v a p o r a t o r. I f t h e
e v a p o r a t o r p r e s s u r e b e c o m e s t o o l o w a n d
t h e r i s k o f e v a p o r a t o r f r e e z i n g o c c u r s , t h e
p n e u m a t i c c o n t r o l v a l v e c o m e s i n t o o p e r a -
t i o n t o r e d u c e t h e c o m p r e s s o r s t r o k e a n d
m a i n t a i n t h e r e q u i r e d e v a p o r a t o r p r e s s u r e .
T h e a u t o m a t i c c o n t r o l m e ch a n i s m c o m e s
f r o m t h e b e l l o w s w h i ch i s u n d e r p e r m a n e n t
v a c u u m o n i t s i n s i d e a n d e x p o s e d t o t h e
s u c t i o n p r e s s u r e o n t h e o u t s i d e . I f t h i s
p r e s s u r e d i ffe r e n t i a l f a l l s t o o l o w d u e t o
l o w s u c t i o n p r e s s u r e t h e b e l l o w s e x p a n d
t o d r i v e t h e n e e d l e t o o p e n t h e c o n n e c t i n g
p a s s a g e b e t w e e n d i s ch a r g e p r e s s u r e a n d
c r a n k c a s e . T h e r e s u l t i n g i n c r e a s e i n c r a n k
c a s e p r e s s u r e l e a d s t o a r e d u c t i o n i n s t r o k e
w i t h t h e c o n s e q u e n t i a l r e d u c t i o n i n r e f r i -
g e r a n t m a s s f l o w r a t e a n d i n c r e a s e i n s u c -
t i o n p r e s s u r e . A s t h e e v a p o r a t o r p r e s s u r e
i n c r e a s e s t h e p r e s s u r e d i ffe r e n t i a l d r i v e s
t h e n e e d l e t o c l o s e t h e c o n n e c t i n g p a s s a g e
b e t w e e n d i s ch a r g e p r e s s u r e a n d c r a n k c a s e .
T h e c r a n k c a s e p r e s s u r e f a l l s a s a r e s u l t o f
t h e s u c t i o n b l e e d a n d t h e c o m p r e s s o r s t r o k e
i n c r e a s e s .
0,4
0,3
0,2
0,1
0,0
Crank Case Pressure - bar
0 2 4 6 8 10 12 14 16
Swash-Plate Angle - radians
Compressor speed: 10 0 0 min-1
Suction pressure: 3 bar
Cur ves marked with head
pressure in bar.
9 12 15
Th e u s e o f ex t e r n a l c o n t r o l g i ve s a n ex t r a
d e g r e e o f f l ex i b i l i t y. P n e uma t i c c o n t r o l ma i n -
t a i n s eva p o r a t o r p r e s s u r e s o t h a t a i r- o ff
t e m p e r a t u r e s r e m a i n a fe w d e g r e e s a b o v e
0 ° C a n d a n y n e e d f o r h i g h e r t e m p e r a t u r e s
t h a n t h i s a r e a ch i e v e d b y m i x i n g w i t h w a r m
a m b i e n t o r r e c i r c u l a t e d a i r. A s a r e s u l t m o r e
c o m p r e s s o r w o r k i s d o n e t o c o o l t h e a i r
d o w n t o t h e l o w t e m p e r a t u r e t h a n i s r e a l l y
n e c e s s a r y. Ve r y s i g n i f i c a n t e n e r g y s a v i n g s
c a n b e m a d e b y u s i n g t h e e x t e r n a l c o n t r o l
t o m a n a g e t h e s y s t e m c a p a c i t y s o t h a t o n l y
s u ff i c i e n t c o o l i n g i s p r o v i d e d t o m e e t t h e
r e a l n e e d s o t h a t s i g n i f i c a n t r e h e a t i n g o f
t h e c o m f o r t a i r i s n o t n e e d e d .
T h i s p o t e n t i a l f o r e n e r g y s a v i n g i s t h e m o s t
i m p o r t a n t a s p e c t o f e x t e r n a l e l e c t r o n i c c o n -
t r o l b u t i t a l s o o f f e r s o t h e r a d v a n t a g e s s u c h
a s d e - s t r o k i n g a t s y s t e m s h u t d o w n s o t h a t
t h e e n g i n e l o a d f e l t b y t h e e n g i n e a t s y s t e m
s t a r t - u p c a n b e g r a d u a l l y i n c r e a s e d – k n o w n
a s “s o f t s t a r t ”. A f u r t h e r a d v a n t a g e i s t h e a b i l -
i t y t o e x e r c i s e a d e g r e e o f c o n t r o l o v e r c a b i n
h u m i d i t y a n d a v o i d e x c e s s i v e d r y n e s s t h a t
c a n o c c u r w i t h s i m p l e p n e u m a t i c c o n t r o l .
F i x e d c o m p r e s s o r s h a v e e l e c t r o m a g n e t i c a l l y
o p e r a t e d c l u t ch e s t o a l l o w s y s t e m c o n t r o l
b y s w i t ch i n g t h e c o m p r e s s o r d r i v e o n a n d
o ff a s r e q u i r e d . Va r i a b l e c o m p r e s s o r s h a v e
t r a d i t i o n a l l y r e t a i n e d t h e c l u t ch t o b e a b l e
t o t u r n t h e s y s t e m o ff w h e n n o t r e q u i r e d o r
s h o u l d s y s t e m c o n d i t i o n s a p p r o a ch u n s a fe
o p e r a t i n g l e v e l s f o r a n y r e a s o n . A m o r e r e c e n t
i n n o v a t i o n i s t h e i n t r o d u c t i o n o f c l u t ch l e s s
c o m p r e s s o r s . I t i s m a d e p o s s i b l e b y t h e
i m p l e m e n t a t i o n o f e x t e r n a l c o m p r e s s o r c o n -
t r o l . H e r e t h e c o m p r e s s o r c a n b e d e s t r o k e d
t o s u ch a n e x t e n t t h a t i t n o l o n g e r p u m p s
a n d c a n b e p e r m a n e n t l y d r i v e n w i t h o u t
d i s s i p a t i o n o f s i g n i f i c a n t e n e r g y. Ty p i c a l
d e s t r o k e d e n e r g y c o n s u m p t i o n i s o n l y 15 0W
a t 3 0 0 0 r e v / m i n . Ve r y s m a l l s t r o k e c a n b e
r e l a t i v e l y e a s i l y a ch i e v e d a n d t h e ch a l l e n g e
i s t o a c t i v a t e u p s t r o k e a g a i n w h e n r e q u i r e d .
T h e a d v a n t a g e s a r e p r i n c i p a l l y p a ck a g i n g
a n d w e i g h t a l t h o u g h c o s t s a v i n g s a r e a l s o
p o s s i b l e .
S e c t i o n t h r o u g h e l e c t r o n i c a l l y
c o n t r o l l e d c o m p r e s s o r v a l v e
SP - fixed displacement
## - displacement in cc/10
SP08
SP10
SP13
SP15
SP17
SP21
Fixed
Delphi engine-driven R134a compressor range
A Compressor Range
One frequently hears a need expressed with phrases such as: ”I want the most efficient and lightest component possible.” In reality however, it is not possible to optimise against two independent parameters at the same time - the most efficient possible will not necessarily be the lightest and vice-versa (other than by coincidence). While optimisation against a single parameter is possible, the significance of the second can only then be expressed as a limit or a constraint. “I want the most efficient component possible weighing less than 1kg.”
It is generally recognised that the automotive industry sources against the single optimisation parameter – cost. While there are very many other constraints within which they have to operate – both applications and market based constraints – these can only be expressed as limiting values. The target will always be to acquire the product that meets the needs of the application at the lowest possible cost. Since the needs expressed as constraints vary greatly, depending upon application, a supplier needs to offer an extensive range of compressors offering a spectrum of balances between sophistication and cost in order to stand a chance of meeting the needs of a significant proportion of the market. This will extend from simple fixed compressors to meet the most straightforward applications to electronically controlled variable compressors where performance, accuracy and efficiency play a more important role.
As means of illustration the Delphi compressor product range for R134a is indicated below. Compressors are shown with the trend for both increasing sophistication and cost going from left to right and increasing displacement going from top to bottom.
The SP range of fixed swash-plate compressors each with five double acting pistons represents the lowest cost solution for applications that can tolerate the implications of a cycling clutch. The double piston configuration means that in effect there are a total of ten compression cavities which yields very low levels of pressure fluctuation. This feature combined with the smoothness of the swash-plate drive results in an inherently quiet compressor.
The V5 range of wobble plate variable compressors has already been described as the original Delphi variable compressor. It has seen con-siderable refinement over the years and whilst it cannot compete with the CVC swash-plate range for quietness and efficiency it represents a very cost-effective introduction to variable compressor technology. The dual PTFE piston rings contribute to low blow-by and good oil retention.
The Compact Variable Compressor (CVC) range of compressors uses swash-plate technology to ensure that a/c system generated noise and vibration is kept to a minimum. Internally and externally controlled versions are available.
The externally controlled range of CVC compressors are offered with and without clutch. In the clutchless compressor the ability to upstroke again after destroke to a minimum that is only 1 or 2% of maximum stroke is ensured by the very tight tolerances of the piston and cylinder bore dimensions. They ensure very low blow-by which helps maintain low parasitic losses and ensure that upstroke can be achieved when required.
Variable
Wobble Plate
Increasing
displacement
Swash-Plate
Increasing sophistication and cost trend
### - displacement in cc
V - wobble plate
# - number of cylinders
i - internal control
e - external control
# - number of pistons
CVC - variable swash-plate
### - max displacement in cc
i - internal control
c - clutchless
e - external control
123V5i
132V5i
144V5i
151V5i
156V5i
156V5e
179V7e
5CVC120i
6CVC125i
6CVC135i
6CVC140i
6CVC160i
7CVC165i
7CVC185i
5CVC120c
6CVC125c
6CVC135c
6CVC140c
6CVC160c
7CVC165c
7CVC185c
5CVC120e
6CVC125e
6CVC135e
6CVC140e
6CVC160e
7CVC165e
7CVC185e
I t c a n b e s e e n t h a t t h e C VC r a n g e i s v e r y
c o m p r e h e n s i v e . N o t s h o w n h e r e i s t h e
f u r t h e r f l e x i b i l i t y o ffe r e d b y a v e r y w i d e
r a n g e o f p o s s i b l e p i p i n g c o n f i g u r a t i o n s
w h i ch t o g e t h e r c a r r y t h e i m p l i c a t i o n t h a t a
l a r g e n u m b e r o f d i ffe r e n t c o m p r e s s o r c o n -
f i g u r a t i o n s m u s t p a s s d o w n t h e p r o d u c t i o n
l i n e s . I t h a s b e e n c o n c l u d e d b y s o m e t h a t
t h i s c o m p l e x i t y i s l i k e l y t o h a v e a n e g a t i v e
e ffe c t o n p r o d u c t q u a l i t y w h e n i n f a c t t h e
o p p o s i t e i s t r u e . To m a n a g e t h e c o m p l e x i t y
a s y s t e m k n o w n a s R F I D – r a d i o f r e q u e n c y
i d e n t i f i c a t i o n – i s u s e d i n w h i ch e a ch i n d i v i d -
u a l c o m p r e s s o r c a r r i e s a ch i p w i t h i t d o w n
t h e p r o d u c t i o n l i n e . D u r i n g t h e p a s s a g e
d o w n t h e l i n e t h e ch i p r e a d s a n d v e r i f i e s a l l
t h e i n f o r m a t i o n a b o u t t h e i n d i v i d u a l c o m p o -
n e n t s a s t h e y a r e a s s e m b l e d ( m a n u f a c t u r i n g
d a t e s , d i m e n s i o n s , e t c ) a n d c o m m u n i c a t e s
i t b a ck t o a c e n t r a l c o m p u t e r f o r f i l i n g . T h i s
d a t a o n e a ch i n d i v i d u a l c o m p r e s s o r i s t h e n
a v a i l a b l e f o r l a t e r a c c e s s s h o u l d t h e r e b e
p r o b l e m s f u r t h e r d o w n t h e l i n e o r p r o b l e m s
f r o m t h e f i e l d . T h e a v a i l a b i l i t y o f a l l t h i s c o m -
p r e h e n s i v e a n d d e t a i l e d d a t a c o n t r i b u t e s t o
t h e e s t a b l i s h m e n t a n d m a i n t e n a n c e o f t h e
v e r y h i g h l e v e l s o f r e l i a b i l i t y r e q u i r e d b y t h e
a p p l i c a t i o n .
N e w T e c h n o l o g i e s
I n r e c e n t y e a r s a s e r i o u s i n t e r e s t i n t h e
u s e o f R 74 4 a s r e f r i g e r a n t i n a u t o m o t i v e
a i r c o n d i t i o n i n g s y s t e m s h a s b e e n g e n e -
r a t e d . E u r o p e a n l e g i s l a t i o n h a s r e c e n t l y
b e e n p a s s e d t h a t w i l l f o r c e t h e i n d u s t r y
t o m o v e a w a y f r o m R 13 4 a a n d R 74 4 h a s
b e c o m e t h e l e a d i n g c o n t e n d e r. A s a r e s u l t
D e l p h i i s d e v e l o p i n g a r a n g e o f s w a s h - p l a t e
c o m p r e s s o r s t o m e e t t h i s n e e d . C u r r e n t
p r o t o t y p e s h a v e f i v e p i s t o n s a n d m a x i m u m
d i s p l a c e m e n t o f 3 0 c c a l t h o u g h t h e n u m b e r
o f p i s t o n s i n t h e f i n a l p r o d u c t r a n g e i s s t i l l
u n d e r d e v e l o p m e n t . B o t h f i x e d a n d v a r i a b l e
v e r s i o n s o f d i s p l a c e m e n t s o f 15 , 2 1 a n d
3 0 c c a r e p l a n n e d . I t i s e n v i s a g e d t h a t f o r
l o w d i s p l a c e m e n t t h e n u m b e r o f p i s t o n s
w i l l b e b e t w e e n 5 a n d 7, a t t h e h i g h e n d i t
w i l l b e b e t w e e n 7 a n d 9 . T h e r e a s o n f o r t h i s
u n c e r t a i n t y i s t h a t t h e a p p r o p r i a t e b a l a n c e
b e t w e e n c o s t a n d n o i s e / d u r a b i l i t y h a s n o t
y e t b e e n e s t a b l i s h e d .
I t c a n b e s e e n t h a t a s a r e s u l t o f t h e v e r y
d i ffe r e n t f l u i d p r o p e r t i e s , t h e d i s p l a c e m e n t s
o ffe r e d a r e v e r y m u ch l o w e r t h a n f o r R 13 4 a .
T h e r a n g e fe a t u r e s s h a ft s e a l i n g b y f a c e s e a l
a n d i n t e r n a l o i l s e p a r a t o r. T h e n e e d f o r t h e
l a tt e r c o m e s f r o m t h e s i g n i f i c a n t e v a p o r a t o r
p e r f o r m a n c e d e g r a d a t i o n t h a t o c c u r s w i t h
C O 2 i f e x c e s s o i l i s a l l o w e d t o c i r c u l a t e .
T h e s e c o n d n e w t e ch n o l o g y c o n c e r n s c o m -
p r e s s o r s f o r f u t u r e p o w e r t r a i n s , w h e t h e r
h y b r i d o r f u e l c e l l – t h e e l e c t r i c a l l y d r i v e n
c o m p r e s s o r. U n d e r d e v e l o p m e n t i s a f a m i l y
o f s c r o l l c o m p r e s s o r s d r i v e n b y 3 15 v o l t
b r u s h l e s s e l e c t r i c m o t o r s . S c r o l l d i s p l a c e -
m e n t s a r e 2 8 a n d 3 8 c c f o r c o o l i n g c a p a c i t i e s
o f 5 . 6 a n d 7. 1 kW r e s p e c t i v e l y. T h e m o t o r s
a r e c o o l e d u s i n g t h e l o w t e m p e r a t u r e r e -
f r i g e r a n t v a p o u r f r o m t h e e v a p o r a t o r w i t h
a r e s u l t a n t m o t o r e ff i c i e n c y o f 9 4% . T h e
i n v e r t e r i s c o o l e d b y c o n d u c t i o n f r o m t h e
s a m e r e f r i g e r a n t a n d i t t o o h a s e ff i c i e n c y i n
t h e 9 4 t o 9 8% r a n g e .
D e l p h i C O 2 c o m p r e s s o r
S e c t i o n t h r o u g h D e l p h i E l e c t r i c C o m p r e s s o r
1 S c r o l l C o m p r e s s o r
2 Pe r m a n e n t M a g n e t M o t o r
3 I n v e r t e r a n d I n t e g r a t e d E l e c t r o n i c s
1 2
3
C o n c l u s i o n
T h i s p a p e r h a s a ime d to p re s e n t t h e te ch n i c a l re q u i reme n t s o f t h e c omp re s s o r fo r u s e i n
a u tomo t i ve a i r c o n d i t i o n i n g a p p l i c a t i o n s a n d to s h ow h ow t h e d i ve r s e re q u i reme n t s o f t h e
a p p l i c a t i o n me a n t h a t a s u p p l i e r mu s t h ave ava i l a b l e a ra n ge o f te ch n o l o g i e s a n d s p e c i f i -
c a t i o n s to b e a b l e to me e t t h e s e n e e d s . I t go e s o n to s h ow h ow t h e D e l p h i c omp re s s o r
p ro d u c t ra n ge i s d e s i g n e d to g i ve c omp re h e n s i ve c ove ra ge a n d f i n i s h e s wi t h c o n s i d e ra t i o n
o f c omp re s s o r s fo r d e ve l o pme n t a l te ch n o l o g i e s t h a t a re l i ke l y to b e c ome s i g n i f i c a n t i n t h e
re l a t i ve l y n e a r f u tu re .
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About Delphi Multi-national: Delphi conducts its business operations through various subsidiaries and has headquarter in Troy Michigan USA, Paris, Tokyo and São Paulo, Brazil.
